Method and mechanism for biaxially orienting extruded tubular film



Dec- 13, 1966 E. .LJUSTUS 329km@ METHOD AND MECHANISM FOR BIAXIALLYORIENTING EXTRUDED TUBULAR FILM Filed May 5, 1964 United States PatentOfiee 3,2%,876 Patented Dec. 13, 1966 3,291,876 METHD AND MECHANHSM FRBIAXIALLY ORHENTNG EXTRUDED TUBULAR FILM Edgar J. Sustus, Beloit, Wis.,assigner to Beloit Corporation, Beioit, Wis., a corporation of WisconsinFiled May 5, 1964, Ser. No. 365,023 7 Claims. (Cl. 264-95) The inventionrelates to improvements in the manufacture of tubular film ofthermoplastic material.

A commonly used method and apparatus for the production of thermoplasticfilm in tubular form involves forming an extrudate of material in aformative plastic state 'and extruding the material through an annulardie to form a seamless tubing. The tubing is received from the die by apair of squeeze or pinch rolls spaced from the point of extrusion, andas the tubing advances to the squeeze rolls and while it is in theformative plastic state it is inflated to a predetermined diameter by lagaseous medium introduced into the interior of the tubing to form abubble. Axial orientation of the tubular film material is obtained bydrawing the material forwardly by the pinc-h rolls `yand can becontrolled by controlling the speed of rotation of the pinch rolls.Biaxial orientation is obtained and regulated -by the inflation of thetubing to a predetermined diameter to form the bubble in the tubebetween the die .and pinch rolls. The present invention is concernedwith the control of the biaxial orientation of the film in an improvedrmanner and with the control of the cooling of the film which begins assoon as the film leaves the die. Exterior cooling is maintainedsubstantially constant due to the constant temperature of the ambientair land interior cooling is controlled by the temperature of thegaseous medium within the film.

It is an object of the present invention to provide an improved methodfor introducing a cooling gaseous medium into -a section of continuousadvancing length of tubular film under controlled conditions foraccurately regulating the biaxial orientation of the film and forobtaining optimum and uniform cooling of the film.

A further object of the invention is to provide .an improved method andapparatus for slitting the edge o-f the tube of film formed by thetubular extr-usion process so as to obtain a sheet of film.

The invention contemplates providing a mechanism for extruding tubularplastic to an extrusio-n die with a pair of rotatable pinch rolls spacedfrom the die for drawing the tubular film forwardly from the die with abubble formed `between the die and pinch rolls, and in a preferredarrangement, an air nozzle projects into the tube at the end of thepinch rolls with a cutting :bl-ade mounted on the nozzle continuouslyslitting the tube, with the fiow of air into the tube controlled tocontrol the pressure within the bubble and therefore the cross grainorientation of the lplastic film.

Other objects, advantages and features will become more apparent withthe teaching of the principles of the invention in connection with thedisclosure of the preferred embodiment thereof in the specification,claims and drawings, in which:

FIGURE l is a schematic elevational showin-g of a portion of mechanismfor extr-uding tubular film constructed and operating in accordance withthe principles of the present invention;

FIGURE 2 is a schematic vertical sectional view taken substantiallyalong line II-II of FIGURE l;

FIGURE 3 is a fragmentary section-al view taken substantially along lineIII-III of FIGURE 2, and

FIGURE 4 is a fragmentary sectional view showing an alternatearrangement.

On the drawings:

Thermoplastic material such as polyethylene is heated and worked to forman extrudate in the formative plastic state in an extruder 10 whichdelivers the extrudate to -a die 11 having a suitable annular opening,The die and extruder lare of the type which will be fully ap preciate-dby th-ose versed in the art and need not be described in detail. Alength of tubular 'film 12 continually emerges from the die 11 andtapers outwardly to form a bubble 13. As is known, the tubular film 12will expand biaxially due to the pressure of la gaseous coolinginfiating medi-um forming the bubble 13. Coolingof the film may beaccomplished by the ambient -air and by an annular air ring embodied inthe member 11 blowing downwardly along the surface of the film. Theplastic will form a frost line at the lower end of the conical portionand the bubble will retain a substantially uniform diameter as it movestoward a pair of pinch rolls 1S and 16. j

The pin-oh rolls are rotated to draw the tubular film from the die andcollapse the bu'bble fo-rming `a attened layer of plastic sheeting 19which is fed to delivery rolls, not shown.

lust following or substantially at lthe pinch rolls 15 and 16 the tu-beis slit at its edge by a knife 22 having a cutting edge facing towardthe advancing tube and continuously slitting the tube. This converts thetube into :a doubled sheet.

Extending upwardly into the interior of the bubble 13 at the end of therolls 16 and 15 and communicating with the interior of the bubble is ameans for inserting the gaseous medium into the bubble, in the form ofan air nozzle or line 2f). The air line is supplied with air at asubstantially constant temperature from .a suitable supply line 21a andthe rate of flow of air and air pressure through the line is regulatedby an air valve 21. Thus the conditions of the air within the bubble asto temperature and pressure are retained substantially constant. Some ofthe air after circulating through the bubble escapes alongside the 4airline 20. The line 20 extends axially into the bubble being aligned withthe nip between the rolls. The line 20 is shaped so that it has anextension or nozzle opening 23 extending up into the tube to insure thatthe air flows up into the bubble. Me-ans for adjusting the verticalposition of the knife 22, and nozzle 23 as shown schematically :by thedouble arrowed line 24 may be provided.

A pair of .guide rollers 25 `may be located ahead of the pinch rolls 15and 16 at Ithe edge olf the bubble 1'3 opposite the location of thenozzle 2,3. Only one roller 25 is shown, for convenience of illustrationrbut two are provided, one on each side of the bubble, in opposedrelationship to slightly flatten the bubble.

The nozzle may be turned inwardly as shown at 23a `in FIGURE 4 so thatair discharge is nearer the center of the bubble rather than adjacentthe film wall.

Thus it will be seen that I have provided an improved method and[mechanism which meets the objectives and advantages above set forthyfor controlling the biaxial orientation of film by regulating theconditions of the air -or other gaseous medium which is injected intothe l-m bubble. The mechanism is relatively simple in construction andreliable in operation and is capa-ble of continuous operation in a filmmanufacturing process without frequent attention or repair.

Control of the size of the bubble in the film is regulated by varyingthe rate of flow of ai-r into the bubble by the valve. The cooling rateis also variable by the temperature of the delivered air.

The drawings and specification present a detailed disclosure of thepreferred embodiments of ythe invention,

and it is to be understood that lthe invention is not limited to thespeciiic forms disclosed, but covers all modiiications, changes andalternative constructions and methods lfalling within the scope of theprinciples taught by the invention.

I claim as my invention:

1. The method of making thin sheet .lrn which comprises extr-udingplastic material continuously from an extruding head lforming a tube,flattening the tube across the width thereof at a flattening locationspaced from the extruding head and leaving an edge portion unilattened,inilating the tfube with an inilating member @through said edge portionfor form-ing a bubble between .the inating head and flattening location,and slitting the edge oli the tube at said edge portion and separatingthe lflattened t-ube to accommodate insertion of the inilating member.

2. A mechanism for extruding tubular plastic 4film comprising,

an extrusion die for extruding film in tubular form,

means for delivering extrudate to said die, a `pair of rotatable pinch.rolls spaced from said die tor drawing .the tubular film from the diewith a bubble be-ing formed between the die and rolls, said rollspositioned relative to the die so that an edge portion of the iilmextends beyond the ends of the rolls,

knife means positioned at the ends of the pinch rolls at said edgeportion od the til-m continuously slitting the film,

an air conduit extending into the slit iilm positioned to discharge airthrough said edge portion past said ipinoh rolls into said bubble ttorinitiating the bubble and biaxially orienting the lilm, and

means in said air conduit controlling the rate of flow of air into theiilm bubble for controlling the degree of biaxial orientation.

3. A mechanism for extnuding tubular plastic lm comprising,

an extrusion die for extruding film in tubular form,

means yfor delivering ext-rudate to said die,

a -pair o-f rotatable pinch rolls spaced from said die for drawing thetubular `ilm from the die with a bubble being for-med between the dieand trolls, and positioned relative to the die so that an edge poirytionof the film extends beyond the Iroll ends,

an air tube projecting axially into the tube at said edge portion beingpositioned opposite the roll ends and aligned with the nip between thepinch rolls, and a cutting blade mounted on the tube and slitting theoncoming tube.

4. A mechanism -or extruding tubular plastic iilm comprising,

an extrusion die tor extruding iilm yin tubular form,

means for delivering extrudate to said die,

a pair of rotatable pinch rolls spaced from said die for drawing thetubular -film from the die with a bubble being formed between .the dieand rolls, said rolls positioned relative to the die so that an edgeportion of the lil-rn is located past the ends of the rolls,

knife means positioned at the end of the pinch rolls at said ed-geportion of the iilrn bubble continuously slitting the lm,

means for adjustably locating ldie position of said knife means relativeto the pinch rolls,

and means communicating with the interior of the bubble through saidedge portion for directing intlating air into the interior thereof andbiaxially orien g the lrn.

A mechanism for extruding tubular plastic film cornprismg,

au extrusion die .for extnudingiilm in tubular form, means fordelivering extrudate to said die,

a pair of rotatable pinch rolls spaced from said die and :having a niptherebetween `for drawing the tubular lm trom the die with a bubblebeing 4tonni-ed between the die and rolls, said rolls positionedrelative to the die so that a portion of the tilm is beyond the endofthe nip and not pinched between the rolls,

fluid delivery means communicating with the interior of the tubular lmthrough said edge portion for iniiating the tube to tor-m the bubble andbiaxially orient the iilm, and means axially slitting the tube at saidedge portion wit-h said fluid delivery means extending through the slitin the iilm.

6. A mechanism ifor extruding tubular plastic lm in accordance withclaim 5 wherein the iluid delivery means is in the form of a tubeextending through said edge portion parallel to the direction ofmovement of the lilm and the discharge end of the tube opens laterallyin the bubble transversely orf the axis thereof.

7. A mechanism for extmding tubular plastic lhlm in accordance withclaim 5 wherein means are provided tor flattening -the bubble ahead ofthe pinch Dolls at the side of the lil-m opposite said edge portion.

References Cited by the Examiner UNITED STATES PATENTS 2,750,631 6/ 1956Johnson 264-95 2,832,994 5/ 1958 Ahlich et al. 264-95 X 2,862,23412/1958 Gerber 264-95 2,923,194 2/1960 Ambler et al.

2,987,767 6/ 1961 Berry et al 264-95 3,092,874- 6/ 1963 Fallwell 264-95X 3,121,761y 2/ 1964 Osborn 264-95 3,166,616 1/1965 Bild et al. 18-145 X3,170,011 2/ 1965 Cheney et al 264-95 3,193,547 7/ 1965 Schott 264-95 XROBERT F. WHITE, Primary Examiner.

L. S. SQUIRES, Assistant Examiner.

1. THE METHOD OF MAKING THIN SHEET FILM WHICH COMPRISES EXTRUDINGPLASTIC MATERIAL CONTINUOUSLY FROM AN EXTRUDING HEAD FORMING A TUBE,FLATTENING THE TUBE ACROSS THE WIDTH THEREOF AT A FLATTENING LOCATIONSPACED FROM THE EXTRUDING HEAD AND LEAVING AN EDGE PORTION UNFLATTENED,INFLATING THE TUBE WITH AN INFLATING MEMBER THROUGH SAID EDGE PORTIONFOR FORMING A BUBBLE BETWEEN THE INFLATING HEAD AND FLATTENING LOCATION,AND SLTTING THE EDGE OF THE TUBE AT SAID EDGE PORTION AND SEPARATING THEFLATTENED TUBE TO ACCOMMODATE INSERTION OF THE INFLATING MEMBER.